Non-linear exciter controller for power system damping

ABSTRACT

Damping of power system oscillations is accomplished by additionally directing exciter-voltage regulation for individual system generators in accordance with variations in the derivative of reactive power generated by a generator. Signal voltage proportional to reactive power in generator output is differentiated to develop a signal voltage representing rate of change of reactive power variations which is applicable as an auxiliary input for determining operational control of excitervoltage regulation of the generator. Control for suppressing system oscillations is continuous as long as generator bus voltage does not exceed pre-set upper and lower voltage limits.

United States Patent Hauf [541 NON-LINEAR EXCITER CONTROLLER FOR POWERSYSTEM DAMPING [72] Inventor: Adolf W. Haul, Bonneville PowerAdministration, Lewiston, Idaho 83501 [73] Assignee: The United Statesof America as represented by the Secretary of the Interior 22 Filed:July 16,1970

21 Appl.No.: 55,541

52 user. ..a22/19,3o7/s4 ,322/2o, 322/24, 322/25 [56] Reierences CitedUNITED STATES PATENTS 2,981,882 4/1961 Rosenblatt ..322/24 [1513,656,048 Apr. 11, 1972 3,474,323 10/1969 Kilgore et al ..322/28 X2,478,623 8/1949 Crary et al. ..322/20 2,872,591 2/1959 Stineman..322/20 X Primary Examiner-Lewis H. Myers Assistant Examiner-H.Huberfeld Attorney-Emest S. Cohen and Gersten Sadowsky [57] 7 ABSTRACTDamping of power system oscillations is accomplished by additionallydirecting exciter-voltage regulation for individual system generators inaccordance with variations in the derivative Of reactive power generatedby a generator. Signal voltage proportional to reactive power ingenerator output is differentiated 'tO develop a signal voltagerepresenting rate of change of reactive power variations which isapplicable as an auxiliary input for determining operational control ofexcitervoltage regulation of the generator. Control for suppressingsystem oscillations is continuous as long as generator bus voltage doesnot exceed pre-set upper and lower voltage limits.

4 Claims, 2 Drawing Figures Patented April 11, 1972 2 Sheets-Sheet lINVENTOR ADOLF H. HAUF ATTORNEY Patented April 11, 1972 2 Sheets-Sheet 2[NYE/V TO)? ADOLF m HAUF R/VEY distribution systems. Performance fromthe disturbance have a small,

BACKGROUND OF THE INVENTION The invention relates to advancements inoperational procedures and equipment for power generating stations whichimprove the performance of power transmission and quality is largelydependent on system stability, or ability to regain equilibriumfollowing periodic system disturbances such as caused by line faultswhich trip out transmission lines causing load losses and otherwisecritically change the power fiow paths of transmission networks andtherewith the power factor and other characteristics of the generatorloads. Voltage control by voltage regulators at the generator stationsis routinely employed to rapidly arrive at a requisite equilibrium.Advances flowing from the invention maintain an improved regulation atthe generating stations which dampens system oscillations and securesoverall systems operating stability. importantly involved is theapplication of a non-linear control which is responsive to reactivepower at generator output terminals and thus a function of the manner inwhich the generator is excited, the length and type of transmission lineused to connect the generator to the load or system, the type ofdisturbance that occurs in a power system and its location relative toeach generator. More specifically, the control is a function of thederivative of the reactive power demanded at a particular power plantsuch that plants in an area of a severe system disturbance have a largecontrol signal applied to their exciter-voltage regulators whereasplants remotely located if any, control signal applied to theirexciter-voltage regulators. Consequently, the total integrated powersystem complete with its behavior determines the control signal at eachplant relative to the contribution by the plant to'the system with theresult that the plant most likely to be lost from the power system dueto a system disturbance automatically receives the largest controlsignal so as to damp the disturbance in an optimal manner.

PRIOR ART Reactive power sensed at generator terminals has been used formaintaining the synchronism of individual generators and accomplishingpower equalization among multiple generators of a system. In a U.S. Pat.No. 2,478,623, granted Aug. 9, 1949 to S. B. Crary et al., is describeda voltage regulator control which in response to a measurement ofreactive power provides an adjustable lower limit on alternator fieldexcitation for protecting the alternator against asynchronism. Thecontrol prevents the field voltage on the alternator from being reducedto a point where due to under-excitation synchronizating torque betweenthe rotor and the stator is such that the alternator will pull out ofsynchronism with the rest of a power system. The apparatus disclosed byCrary et al. is therefore a protective device for a single alternatorbecoming operatively efiective only when voltage regulation actioncritically decreases field excitation. Power equalization apparatusdisclosed in a US. Pat. No. 2,872,591, granted Feb. 3, 1959, to R. W.Stineman provides reactive power sensors and responding control forindividual alternators of a paralleled alternator system wherein eachreactive power sensor is connected to receive input signals from morethan one alternator. As a result, the corrective signal generated forimpression on the exciter field winding of the individual alternatorsmaintains the reactive power equally divided among the alternators whilemaintaining system voltage at a predetermined regulated value.

It is evident that in the utilization of reactive power as a controllingfactor in directing alternator operation, as exemplified by the patentedarrangements previously considered, there has not been recognized thatthe derivative of reactive power can be effectively applied to determinesystem stabilization control. Heretofore, power system frequency wasgenerally used to determine a control variable for system stabilization.

1969, to F. R. Schleif et al. is representative of an advanced form ofthis type of system stabilization control. However, effective systemstabilization control based on power system frequency cannot bemaximized since the amplitude or rate of change of frequency isrelatively the same at each plant. Thus, in applying corrective controlquantities to power plants of a system such stabilization control failsto assign the control quantities among the power plants in accordancewith the magnitude or scope of the disturbance affecting the individualplants. On the other hand, the present invention provides for theproduction at each power plant of a corrective control quantity which isproportional to the derivative of the reactive power signal amplitude atthe plant and thus corresponding to operational conditions at the plantas well as the relative stability conditions in the overall systems.

SUMMARY OF THE INVENTION Optimum power system stability is achievedthrough damping swing oscillations in system power flow by a uniqueauxiliary exciter control on the system generators. In a three phasepower system the output terminals of each generator have connectionsthereto, made by way of three phase potential and current transformers,from a transducer which is adapted to produce a voltage proportional tothe reactive power (VAR) generated by the generator. Following filteringand amplification of the VAR signal, in a conventional manner, thesignal is processed through further amplification in a dififerentiatorplus a wash-out response which determines an amplified signalrepresentative of the VAR rate of change which decays exponentially witha time constant equal to the amplifier combination time constant. Anexciter control quan tity thus produced is fed to a driver whose outputis controlled by a logic controlled limiter which is designed to protectthe alternator terminal Voltage from becoming too high or too low. Thedriver output is fed to the input of the exciter-voltage regulator,usually a magnetic amplifier, for the generator which in a conventionalmanner establishes the generator output as a function of the regulation.Since the reactive power measured by the VAR transducer is a function ofthe terminal voltage a closed control loop is formed which enables acontinuing stabilizing action to become part of the regular voltageregulation control on the generator. An adjustable exciter compensationfacility is additionally provided in the auxiliary exciter control toboost feedback gain where exciter response drops off too rapidly;

It is therefore a primary object of the present invention to provide animproved stability control procedure for the operation of electricalpower generator systems which is based on a function of reactive powerin the generator output.

This and other objects and advantages of the invention will become morefully apparent from the following description of a preferred embodimentof the invention when considered together with the accompanying drawingin which FIGS. 1A and 1B taken together constitute a schematicrepresentation of electrical connections and components interrelatedthereby constituting the embodiment of the invention as adapted forcooperation with a power system generator.

Reference is made to the schematic showing of the drawing whererepresentations of two AC generators l0 and 12, and transformerconnections 14 coupling the generators to a system network 16 by way ofa branch line 18, are intended to indicate a power system in which thepresent invention is operable to effect stabilization. Generators 10 and12 have operatively associated therewith voltage regulating equipment 20and 22, respectively, each comprising an exciter (not shown) whichsupplies load compensating control voltage to the field windings of thegenerators by way of connections represented by leads 24 and 26,respectively. Voltage regulators of the type indicated are conventionalin the art, and for a more detailed disclosure thereof reference may bemade to the previously identified patent to Schleif et a1. Regulatorsand 22 are supplied on leads 28 and 30, respectively, with generatorterminal voltages, in the usual manner, and additionally on lines 32 and34, respectively, with auxiliary control voltages which are derived foreach generator in the controller associated therewith in accordance withthe present invention. S Since a controller according to the inventionis cooperatively related with each generator of the system in the sameway, an exemplary disclosure herein is limited to the controller 40 ofgenerator 10.

A measurement of reactive power in the three phase, four wiredistribution line 42 from the output terminals of generator 10, is takenby a VAR transducer 44 coupled a line 42 by a wire bundle of 10 leadsrepresented by the X extension of line 46. Lines 48 and 50 appear in thedrawing to indicate that bundle 46 comprises connections to threecurrent transfob mers, and a three phase, four wire potentialtransformer in line 42 which connects the transducer to generator 10.Transducer 44 produces as an output signal on a lead 51, to aconventional twin T notch filter 45 tuned to the transducer ripplefrequency, the output of the filter on a lead 52 being a DC voltagewhich is proportional to the three phase reactive power of thegenerator. The type of VAR transducer employed must be compatible withthe type of power system involved. A one element device such asdisclosed by US. Pat. No. 3,218,554, granted Nov. 16, 1965, to A. J.Corson, in its FIG. 5, is applicable to a single phase power system, anda two element device such as disclosed in FIG. 6 of the Corson patentwould have utility in a three phase, three wire power system. The threephase, four wire power system of the present disclosure requires a threeelement transducer in the nature of that manufactured by ScientificColumbus, Inc., of Columbus, Ohio, as its model VT34-2K5. Also havingutility in connection with the present invention, where unbalance in oneof the phases to neutral is not a problem, is the transducer disclosedby U.S. Pat. No. 3,286,178, granted 1. P. Ultcht, in its FIG. 1.

The reactive power signal is preamplified in a DC operational amplifier54 which receives this signal at a non-inverting input terminal thereofby way of a circuit path including filter lead 52 and a lead 56. Anormally closed service switch 58, and an input resistor 60 for thepreamplifier complete the circuit path. An energizing circuit foramplifier 54 includes leads 62 and 64, respectively, connected to thepositive and negative of a DC source, and having further of to by-passcircuits equipped with capacitors which return to a general ground in aconventional manner and operate to smooth variations in the supplyinput. When amplifier 54 is operational, at a typical gain of 100,feedback supplied to its inverting terminal is derived from amplifieroutput on a lead 66, and applied by way of leads 68 and 70 havingconnected therein a feedback resistor 72. Overall gain for the amplifieris chosen, by changing resistance60 or resistance 72, as a function ofthe generator being controlled, and the amount of control action that isdesired. Reduction of high frequency noise is achieved in a conventionalmanner with a filter capacitor 74 in a parallel feedback connection on alead 76. Since the response of the exciter-voltage regulator, and theregion of frequencies of interest in the control loop associatedtherewith, is below 1 Hz. this filter circuit is tuned above the 1112.level to remove noise from the operational amplifier which would onlysaturate the amplifier. The inverting terminal of amplifier 54 isreturned to ground by way of the feedback connections thereto includingan extension of lead 70 having a resistor 78 connected therein whichminimizes amplifier voltage offset.

The preamplifier signal on lead 66 is also received on a connecting lead80, and through a resistor 81 is introduced to a differentiatingarrangement 82. A summer operational amplifier 84 of the arrangement issupplied at an inverting input terminal thereof with the signal on lead80, and the signal at its output terminal which is carried by way of afeedback circuit through a lead 88 having a resistor 90 connectedtherein. The

. non-inverting input terminal of amplifier 84 receives feedback inputby way of integrator circuitry of arrangement 82 wherein an amplifier 92is operational with a feedback therefor on a lead 94'having anintegrator capacitor 96 connected therein. Input to an invertingterminal of amplifier 92 includes the output of amplifier 84 which issupplied thereto through a potentiometer 98 connected in a lead 100extended from lead 86, and further connections from the contact am ofthe potentiometer on a lead 102 having an input resistor 104 connectedtherein. A non-inverting input terminal of amplifier 84 is supplied withthe integrator output by way of a lead 106 having an input resistor 108connected therein. Amplifiers 84 and 92 have conventional energizinginputs having leads to which by-pass capacitors are connected incircuits to ground. To amplifier 92, at a non-inverting terminalthereof, is further connected a circuit to ground in which a resistor isconnected to minimize voltage offset. Thus amplifiers 84 and 92 arearranged to produce a voltage representing a differential quantitycorresponding to the rate of change of the reactive power in generator10. However, the derivative is relatively pure only up to apredetermined point in frequency whereupon it is no longer thederivative of the input and degrades in a wash-out effect.

Potentiometer 98 is settable to determine a time constant, tau, for theaforesaid wash-out effect which is appropriate of the operatingcharacteristics of generator 10. As indicated, the combined effect ofamplifiers 84 and 92 produces as output on lead 86 the true derivativeof the input on lead 66 when the frequency of this input isapproximately less than l/21r tau Hz. When this frequency is exceededthe derivative action is slowly lost or washed-out with increasingfrequency and the output is representative of a derivative plus a lagfunction. Such operational behavior is desired and necessary so that theVAR feedback loop around the voltage-regulator excitor does not make theregulator action unstable at high frequencies. Potentiometer 98 isproportional to l/tau, and adjustable to set the point in frequencywhere the control function washes out from correspondence to a purederivative to a derivative plus a lag function. The amplifier gain ofthis operation is set to 1.0 so that the high frequency noise generatedin the circuit would not be amplified and then differentiated to producean even larger amplitude of noise.

The reactive power response signal available on lead 86 is' transmittedby way of a connecting lead to a switch 154 and by way of a connectinglead 121 to a switch 159 from where a connecting lead extends to gaincontrol circuit 122 comprising a variable gain amplifier 124. A signalreceived at a non-inverting terminal of amplifier 124 is determined by apotentiometer 126 connected in lead 125 and equipped with a settablecontact in a circuit to the amplifier terminal comprising an inputresistor 128 in a lead 130. Feedback from an output lead 132 of theamplifier to an inverting terminal thereof is provided by way of circuitcomprising a lead 134 in which are connected fixed and adjustableresistors 136 and 138, respectively. A further connection to theinverting terminal is grounded through a resistor 140 adapted tominimize voltage offset. Thus an amplifier voltage output on lead 132 ispredetermined to have a gain in a range from O to 50 by settingattenuator gain at potentiometer 126, and adjusting feedback variablegain at resistor 138.

Provisions made to boost the gain characterizing input to amplifier 124in the event the frequency response of the exciter-voltage regulator andthe alternator tied thereto decreases at frequencies where control isstill desirable and there are sufficient gain and phase marginsremaining, include exciter response compensator arrangements and 151.These arrangements being identical, a detailed description thereof isgiven by way of reference to only arrangement 150. The reactive powerresponse signal on lead 86 also appears as input to the invertingterminal of a summer amplifier 162 in an input circuit comprising aresistor 164 between leads 168 and 169. Compensator control is enabledby presettable feedback circuitry which extends between lead 168 at theamplifier 162 input and lead 157 at the amplifier output, and includeslead 172, a gain control potentiometer 174, input resistances 176 thefrequency rises toward frequency (0,.

l 80f from normal so as to insure that the control behave as a lagfunction. Potentiom eter 180 is used 182 is essentially a combination ofan integratonamplifier 192 and a variable gain, inverting summeramplifier 194. The signal effective at the input terminal of amplifier192 is a summation of the voltages sensed at control potentiometers 174and 180, and discharge from a feedback capacitor 194 in a lead 196 ofthe integrator circuit. Output of the integrator on a lead 198 isreceived, by way of an input resistance 200, at the inverting inputterminal of amplifier 194. A feedback circuit for amplifier 194 includesin a lead 204, a feedback resistor 206, and an adjustable feedbackresistor 208. Each of the network amplifiers is further equipped at anon-inverting terminal thereof with a voltage offset circuit, of thetype previously described. Operational power is supplied to theamplifier from positive and negative terminals related to ground by wayof capacitors in circuits of the type also previously described.

Amplifiers 162, 192, and 194 cooperate in the combination of circuitryconstituting arrangement 150 to generate a leadlag function which isapplicable to compensate the frequency response of the exciter-voltageregulator and the generator field winding at high frequencies above theroll off point frequency 0,. Compensation is thus provided since gain ofthe feedback loop, comprising the instant VAR controller, increases asfrequencies rise from frequency w, to a higher frequency (0,, whereasthe gain of the exciter-voltage regulator.

and the AC machine, constituting the forward loop, drops as relationshipis reflected in phase shift which in the feedback loop is supported bythe lead-lag compensation to compensate for the phase shift in theforward loop. More-particularly proper adjustment of the lead-lagcompensation requires the product of the gain in the forward path andthe feedback path to be less than 1.0 when the phase of the VARapproaches loop is stable. Potentiometer 174 is used to adjustcompensation arrangement 150 for a frequency 341 rising above frequencyw, to the point in frequency where the lead-lag function starts to toadjust arrangement 150 for a frequency dropping below frequency to, andtoward frequency w, to the point in frequency where the lead-legfunction starts to behave as a lead function only. Potentiometer 208,which controls the gain of amplifier 194, in effect shifts bothfrequency points to, and w 2 together in the frequency spectrum. Usuallyfrequency point 00 is set equal to 0,. Once potentiometers 174 and 180are adjusted as indicated potentiometer 208 is operable to allow both w,and 10 to be shifted in frequency together and yet maintain the relativedecade spacing of these frequencies. Compensation is thus easilyadjusted and tuning the control loop for stable operation isfacilitated.

Gain control circuit 122 generates a signal for regulating the operationof a magnetic amplifier 220. However, this signal is effective only aslong as a limiter control relay 222 is energized to maintain its contact224 closed in a circuit comprising a lead 226 which connects magneticamplifier 220 to a biasing network 228 therefor. Relay 222 remainsenergized during a predetermined range of conditions as interpreted by alogic circuit 230, to be hereinafter more fully explained. The controlexercised by biasing network 228 over magnetic amplifier 220 is in turndetermined by the output of amplifier 224 on lead 132. Positive voltageat terminal 232, and negative voltage at terminals 234 and 236, energizenetwork 228 by way of leads 238, 240, and 242. Further leads 246 and 248extend a circuit from amplifier output lead 132 to between the cathodeand anode of a pair of diodes 250 and 252, respectively, which 162 incompensator A corresponding act to protect the amplifier from surges inthe magnetic amplifie'r 220 voltage. Network 228 additionally includesvoltage presetting circuitry in which a potentiometer 254 connectedbetween power terminal leads 238 and 242, comprises a contact arm in alead 256, containing a resistor 258, extending from magnetic amplifierinput lead 226. Also included is a potentiometer 260, in amplifieroutput lead 132, which comprises a contact arm in a lead 262 connectedto magnetic amplifier input lead 226 by way of lead 256. Whereas a basiccontrol potential for magneticamplifier 220 is presettable by adjustmentof potentiometer 254, adjustment of potentiometer 260 presets the rangeof current values deliverable to the magnetic amplifier from the controloutput produced by amplifier 12 1.

Amplifier 124 is responsive to compensator voltage when connectorswitches 154 and 159 are open, and connector switches 152 and 1153,together with connector switches 163 and 155 are closed. The polarityconnection on lead 226 to magnetic amplifier 220 is dependent uponwhether compensator arrangement is used along or along with arrangement151. On the other hand the frequency and phase response of theexcitor-voltage regulator and the alternator, or forward loop, mayindicate that no compensation is necessary. In that case connectorswitches 152, 153, 163 and are opened, and connected switches 154 and159 are closed, such that the compensator arrangements are removed fromthe controller. If it is found from the aforesaid response that onecompensator arrangement is desirable, then connector switch 154 isopened, and connector switches 152 and 153 are closed together withswitch 159. Since connector switches 163 and 155 are left open,compensator arrangement 1S1 remains removed from the controller. As waspreviously indicated, connection of lead 226 to magnetic amplifier 220must be made with a polarity which is compatible with the extent ofcompensator connections made in each instance.

The overall adjustable gain of the complete loop is essentiallycontrolled by circuitry of driver-limiter amplifier 124. This control isaccomplished by adjusting potentiometer 126 and potentiometer 138individually or together. In the disclosed structural embodiment theseadjustments allow for a variation of a factor of 50.0. Since thepreviously described preamplifier has a fixed gain of 100 the total loopgain may be varied from 0 to 5,000 by the aforesaid adjustments. Gain ischosen to complement a particular generator and exciter-voltageregulator, and can be increased or decreased by selecting suitableresistors for the amplifiers, as for example resistor 60 or 72 inamplifier 54, resistor 128 or 138 in amplifier 124, and resistor 81 or90 in amplifier 84. An additional non-inverting amplifier is connectableto the control loop in an obvious manner if the aforesaid componentchanges are not sufficient to yield the desired gain. When thecontroller disclosed herein is to be installed on a particular ACmachine, a magnitude and a phase plot is made of the exciter-voltageregulator and the v AC machine to its terminals. This magnitude andphase plot dictates the maximum control loop gain and phase shift inorder to insure that the combined system remains stable with the controlloop in service.

Logic circuit 230 is essentially a comparator arrangement wherein onephase voltage at the output from generator 10 is compared to voltagescorresponding to preset upper and lower limits for generator regulation.Accordingly, a voltage sensed across a generator phase output isinitially processed in conventional rectifier and filter circuitry 270.The rectified and filtered output supplied on output lead 272 is appliedacross separate input resistors 273 and 275 respectively connected inleads 274 and 276, which constitute input connections to conventionalcomparator circuits 278 and 280, respectively. Predetermined lower andupper voltage limits are set by adjustments of negatively energizedpotentiometers 282 and 284, respectively, so as to determinecorresponding currents on leads 286 and 288, respectively, havingconnections to leads 274 and 276 whereas such currents are compared withcurrents representing generator output as determined by resistors 273and 275. Comparator output components 290 and 292 function in accordancewith the resultant bias current to produce logic output voltages onleads 294 and 296. An OR-circu'it 298 is provided to receive the logicvoltage from comparator 278 directly by way of lead 294, and resistor305, and from comparator 280 by way of lead 296 and a logical invertercircuit 300 therein, having an output on a lead 302 containing aresistor 304. Any operation wherein the generator voltage is less thanthe lower limit, and therefore also less than the upper limit, positivevoltages appear on leads 294 and 296, whereas lead 302 is at zerovoltage, and an output lead 306 of OR-circuit 298 is at a positivevoltage. On the other hand, when the generator voltage is greater thanthe upper limit, and therefore also greater than the lower limit, leads294 and 296 are at zero voltage, and a positive voltage appears on lead302, as well as an OR-circuit output lead 306. However, when thegenerator voltage is between the voltage limits, that is less than theupper limit setting, and greater than the lower limit setting, lead 294is a zero voltage, a positive voltage appears on lead 296, and sincelead 302 is then at a zero voltage, the resulting voltage on OR- outputlead 306 is also at zero. Logic. circuit control over relay 222 iseffectuated by way of a switching circuit comprising a firstNPN-transistor 310 which controls the conductivity of a secondNPN-transistor 312 through a collector to base connection 314 betweenthe respective transistors. Collector voltage for transistor 310 istaken at a positive supply terminal 316 and applied across a resistance318 connected in a lead 320 reaching the collector of transistor 310.The emitters of both transistor are grounded.

During the time generator voltage remains within the presetpredetermined limits, a connection from the OR-circuit output lead 306to the base of transistor 310, applies zero voltage at the base so as toeffectively inhibit conduction through the transistor. Consequently, thepositive potential on lead 320 is applicable to lead 314, and thus seenat the base of transistor 312. The resultant conduction through thecollector-emitter of transistor 312 establishes a current path to groundfor a circuit comprising leads 322 and 324, in which limiter relay 222is energizable from a positive power source terminal 326. In the eventgenerator voltage is beyond either limit, the positive voltage on lead306 at the base of transistor 310 establishes conduction throughresistor 318 by way of the collectoremitter of the transistor. Thevoltage drop across resistor 318 negatively biases transistor 312 so asto prevent conduction therethrough. As a result energization of relay222 is interrupted, and the relay de-activates. Lead 322 in the relaycontrol circuit is equipped with first and second switches 330 and 332,respectively, to permit on and off control of the present invention fromremote locations such as central control units in a power house or acontrol room. In the normal course of operation a continuingenergization of relay 222 maintains its contact 224 closed so as tofacilitate a constant control input from the system of the invention tomagnetic amplifier 220. Variable output from magnetic amplifier 220reaches the exciter controller 20 of generator 10, by way of lead 32,and the stabilizing influence of the exciter control is additionallyestablished in accordance with the auxiliary control of the non-linearvariation of the derivative of the reactive power sensed at thegenerator output terminals. Moreover, as is well understood in the artrelating to the present invention, cut-off of the aforesaid auxiliarycontrol in accordance with the operation of the previously disclosedlogic circuit, is desirable at the upper limit to prevent arcing in thegenerator, and at the lower limit to avoid a critical loss of generatorfield current.

While preferred forms of the method and physical embodiment of theinvention have been illustrated and described herein, it is understoodthat the invention is not limited thereby, but is susceptible to changein form and detail.

What is claimed is:

l. Phased power system damping apparatus, providing an auxiliary excitercontrol for at least one AC generator of said power system wherein anexciter-voltage regulatoroperatively associated with said generatorcomprises a magnetic amplifier,

said apparatus comprising a reactive power transducer operable to sensethe reactive power generated by every phase of said generator andproduce a voltage output corresponding to variations in said reactivepower, a differentiating circuit arrangement operable in response toinput thereto of said reactive power variation voltage output to producea differentiator voltage output representative of the rate of change ofsaid reactive power variations voltage input thereto, further amplifiermeans comprising an operational amplifier having adjustable overall gaincontrol means including an adjustable feedback resistor providing arelatively wide range of gain control, and voltage and currentpresettable means including a biasing network control, said adjustableoperational amplifier being responsive to input of said reactive powervariations rate of change voltage output for producing a voltage appliedto said presettable biasing network which in turn determines voltageoutput applicable as a controlling voltage input to said magneticamplifier whereby said magnetic amplifier is effective accordingly toproduce a control voltage in said exciter-voltage regulator.

2. The apparatus of claim 1, further comprising a circuit connectionthrough which said controlling voltage output of said biasing network isapplied to said magnetic amplifier, a

relay having normally open contacts in said circuit connections, apresettable logic network adapted to control the operation of saidrelay, said logic network including means sensing the output .voltage ofsaid generator and producing a representative voltage therefor, separateadjustable voltage driving means settable to represent a lower limit anda higher limit of said generator output voltage, respectively, betweenwhich limits said auxiliary exciter control is adapted to be effective,means separately comparing said generator output representative voltagewith said respective limit representing voltages, and means includingswitching means responsive to the outputs of said comparing means toproduce an output voltage only when said generator output representativevoltage is between said limit representing voltages, whereby said logicnetwork input voltage is applicable to energize said relay and close thecontact thereof in said circuit connections.

3. The apparatus of claim 1 further comprising adjustable phase lead-lagcompensating networks whereto said reactive power variations rate ofchange voltage is initially supplied and the gain thereof modifiedtherein in response to frequency increases beyond a basic operationalfrequency therefor, and wherefrom said modified reactive powervariations rate of change voltage is supplied as said input to saidoperational amplifier of said further amplifier means.

4. The apparatus of claim 3 wherein said lead-lag compensating networksinclude a phase lag function gain adjustment means settable tocompensate for the effect of frequencies rising above a predeterminedfrequency increase beyond said basic operational frequency, and a phaselead function gain adjustment means settable to compensate for theeffect of frequencies dropping below a predetermined frequency increasebeyond said basic operational frequency.

1. Phased power system damping apparatus, providing an auxiliary excitercontrol for at least one AC generator of said power system wherein anexciter-voltage regulator operatively associated with said generatorcomprises a magnetic amplifier, said apparatus comprising a reactivepower transducer operable to sense the reactiVe power generated by everyphase of said generator and produce a voltage output corresponding tovariations in said reactive power, a differentiating circuit arrangementoperable in response to input thereto of said reactive power variationvoltage output to produce a differentiator voltage output representativeof the rate of change of said reactive power variations voltage inputthereto, further amplifier means comprising an operational amplifierhaving adjustable overall gain control means including an adjustablefeedback resistor providing a relatively wide range of gain control, andvoltage and current presettable means including a biasing networkcontrol, said adjustable operational amplifier being responsive to inputof said reactive power variations rate of change voltage output forproducing a voltage applied to said presettable biasing network which inturn determines voltage output applicable as a controlling voltage inputto said magnetic amplifier whereby said magnetic amplifier is effectiveaccordingly to produce a control voltage in said exciter-voltageregulator.
 2. The apparatus of claim 1, further comprising a circuitconnection through which said controlling voltage output of said biasingnetwork is applied to said magnetic amplifier, a relay having normallyopen contacts in said circuit connections, a presettable logic networkadapted to control the operation of said relay, said logic networkincluding means sensing the output voltage of said generator andproducing a representative voltage therefor, separate adjustable voltagedriving means settable to represent a lower limit and a higher limit ofsaid generator output voltage, respectively, between which limits saidauxiliary exciter control is adapted to be effective, means separatelycomparing said generator output representative voltage with saidrespective limit representing voltages, and means including switchingmeans responsive to the outputs of said comparing means to produce anoutput voltage only when said generator output representative voltage isbetween said limit representing voltages, whereby said logic networkinput voltage is applicable to energize said relay and close the contactthereof in said circuit connections.
 3. The apparatus of claim 1 furthercomprising adjustable phase lead-lag compensating networks whereto saidreactive power variations rate of change voltage is initially suppliedand the gain thereof modified therein in response to frequency increasesbeyond a basic operational frequency therefor, and wherefrom saidmodified reactive power variations rate of change voltage is supplied assaid input to said operational amplifier of said further amplifiermeans.
 4. The apparatus of claim 3 wherein said lead-lag compensatingnetworks include a phase lag function gain adjustment means settable tocompensate for the effect of frequencies rising above a predeterminedfrequency increase beyond said basic operational frequency, and a phaselead function gain adjustment means settable to compensate for theeffect of frequencies dropping below a predetermined frequency increasebeyond said basic operational frequency.